Deep in a flooded uranium mine in Germany, bacteria are doing something scientists thought was nearly impossible: they are locking toxic uranium into a stable form that no longer dissolves in water. Researchers fed the microbes glycerol, and within 130 days, about 95 percent of the dissolved uranium vanished from the water, transformed into a compound so stable it had rarely been seen before.
The discovery, published in Nature Communications, comes from a team at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), working with Wismut GmbH and the University of Granada in Spain. They collected water from a flooded mine in the Ore Mountains, where uranium mining once thrived. The water was rich in dissolved uranium, a heavy metal that becomes mobile and hazardous when mining disturbs its natural mineral state.
Bacteria Eat Uranium and Spit Out a Solid
Bacteria are known to break down all sorts of waste, but uranium is a surprise on the menu. Dr. Evelyn Krawczyk-Bärsch, a scientist at HZDR, explained that some bacteria can use dissolved uranium for their metabolism when glycerol is available as a food source. Glycerol is a simple compound found in fats and can form naturally when fungi decompose wood.
In the lab, the team added glycerol to the mine water and kept it in an oxygen-free environment, mimicking the conditions nearly 2,000 meters underground where oxygen is scarce. The bacteria thrived and, in the process, converted the dissolved uranium into a solid compound that settled out of the water. The uranium ended up concentrated in the bacterial cell walls, where it formed nanoparticles.
A Rare Chemical State That Lasts
The key finding is that the uranium entered a chemical state previously thought to be only temporary. This stable form resists dissolving back into water, which means it could stay locked away for a long time. The researchers were surprised to see it persist, as earlier studies had suggested such compounds would quickly break down.
For local communities in the Ore Mountains, this matters because uranium mining left a legacy of contaminated groundwater. Wismut GmbH, the company that once operated the mines, is now responsible for cleaning up the site. The bacteria offer a potential low-cost, natural method to reduce uranium levels in water without harsh chemicals or energy-intensive treatments.
The study is still basic research, but it opens a door. If scientists can understand how these bacteria work, they might be able to encourage them to clean up other contaminated sites. The next step is to test whether this process can be scaled up from the lab to real-world conditions, where water flows and other organisms compete.
For now, the discovery adds a new tool to the environmental cleanup toolkit: a tiny organism that eats a toxic metal and turns it into stone.
